Guided free film distillation method



M1924, 1943- s. w. FERRls ErAL l 2,447,746

GUIDED FREE FILM DISTILLATION METHOD "13 9 -is' n 11' T yu/ F Fyure 1 Fyfure .2A

y-ll'fveni'ora' i se our PY. Ferris' es Edvard H. Lanu'on' mamy ug. 24, 1948. s. w.l FERRls Erm.

GUIUED FREE FIL DISTILLATION METHOD 2 Sheets-Sheet 2 Filed Jan. 29, 1 945 tamed Aug. 24,1943

GUIDED FREE FILM DIS'I'ILLA'IIONv METHOD Seymour W. Ferris, Mount Holly, N. J., and Edward R. Lamaon. Batboro, and Douglas M. Smith, Norwood, Pa.. assllllorl to The Atlantic Benning Company, Philadelphia, Pa., a corporation of Pennsylvania l The present invention relates to a, method for evaporative distillation, and relates more particularly to a methodfor short path distillation of organic substances under reduced pressure.

It has been proposed heretofore to carry out short path distillation under low pressure by providing a heated vaporizing surface and a condensing surface adjacent thereto, and supplying to the vaporizing surface, the material to be distilied. Since the vaporizing surface wasV invariably at a higher temperature than the material charged to it for vaporization. partial decomposition of the material usually resulted, with the attendant deposition of carbonaceous material upon the vaporizing surface, and this despite the very low pressures usually employed.

'It has also been proposed heretofore to effect short path distillation under low pressure by jetting or spraying the material to be distilled between a source of radiant heat and a condensing surface,` such material forming an unconfined an amount suiilcient to vaporize at least a portion oi said spray or illm. Since the material jetted or sprayed .between the heat source and the condensingsurface was unconfined, diiiculty was encountered in controlling the spray or film and in preventing the unvaporized portions thereof from falling either upon the heat source or upon the condensing surface, and thereby decomposing upon the heat source or contaminating the distillate upon the condensing surface.

The above mentioned and other diiiiculties have been overcome in accordance with the present invention by supplying the heat of vaporization to the material to be distilled prior to form. ing same into a vaporizing iilm, thereby eliminating the use of a superheated vaporizing surface, and by supporting the vaporizing film of distiliahie material during its passage adiacent the condensing surface, thus avoiding contamination of the distillate with unvaporized material.

The method and apparatus of the present invention is adapted for use in the distillation of a wide variety of materials, and particularly in the evaporative'or short path distillation of petroleum distiliates, lubricating oils, residuums, petrolatum, wax, petroleum acids, and oils containing soaps such as the alkali and alkaline earth metal soaps of naphthenic and sulfonic acids. Examples of other materials to which the present invention may be applied with advantage are animai and vegetable oils, fats, waxes, and concentrates thereof, and organic mixtures containing therapeutically active materials. The present application .mmm zo, 194s, semi No. 575.106 i f 4 claim. (ci. 'zoe-s4) invention is also of advantage in separating and purifying hormones, vitamins, enzymes, and the like from materials containing them, such as fish oils, corn oil. cottonseed oil, wheat germ oil, fatty vegetable extracts, etc.

In accordance with this invention. the organic material to be distilled is brought to a vaporizing temperature and formed into a continuously spray ornim capable of absorbing radiant heat'in i p introduction into the distilling vessel.

flowing illm which is supported at its vertical edges during its travel through a distilling vessel in close proximity to and out of contact with a condensing surface, the pressure within the vessel preferably being subatmospheric. In its passage through the vessel. components of the film are 4vaporized and the resulting vapors are condensed and separately withdrawn from the vessel. Undistilled residual material is likewise separately withdrawn, and all or a portion thereof may be recycled for further distillation. The condensing surface employed may be a solid surface suitably lcooled, or may comprise one or a plurality of supported films of condensing liquid of the same or different composition as the vapors to be condensed. When distillation is effected at very low pressures, the organic material to be distilled may be relieved of dissolved or cccluded gas prior to While the present invention is particularly adapted for the distillation of materials at reduced pressure, such invention may also be applied in distillation at atmospheric or superatmospheric pressure.

The present invention may be further under' stood with reference to the accompanying drawing, in which Figures l. 2. and 3 show diagrammatically apparatus suitable for carrying out the distillation process.

Referring to Figure i, a vertical cylindrical chamber I enclosed in jacket 2 is provided with a partition I covering the cross-section of the chamber. The partition 3 is pierced with a plu rality of apertures l extending in a line across the diameter of the partition. Disposed vertically within the chamber I are two support rods l spaced horizontally from one another, one rod at each end of the row of apertures I. On the side wail of chamber i are provided a plurality of annular troughs t spaced vertically from one another and extending completely around the chamber. The troughs are provided on one side with valve-controlled drawoif pipes 'l for withdrawing individual condensate fractions, and on the opposite side with valve-controlled drawoif section of chamber I below partition 3 is provided a relatively large diameter pipe il connecting with means for reducing the pressure within the chamber. Such means (not shown) may comprise any suitable vacuum pump such as a mercury vapor pump, steam ejector pump, mechanical vacuum pump or a combination of suchA umps. i ,l p In operation, a distlllable organic substance. for example, a viscous hydrocarbon oil is supplied from a source not shown through valvecontrolled pipe II and is pumped by pump I2 through tubular heater I3 wherein the temperature of the oil is raised, forexar'nple, to 850 F. Since it is desired to condct the distillation at a low pressure and since the charge oil contains dissolved or occluded gas, such oil-after leaving heater I3 is delivered by valve-controlled pipe Ilto the degassing chamber I connected by pipe I5 to a vacuum pump not shown, The degassing chamber is of conventional design and operation, and requires no further description. The heated oil, in passing through the de gasslng chamber I5 is subjected to reduced pressure and is relieved of its dissolved gas and any highly volatile hydrocarbons which it may have contained. The heated, degassed oil is then 4 gas, the degassing chamber I l may be bypassed and the heated oil introduced through valvecontrolled pipes 2l, and I'I into the distributing section of chamber I. If the distillation is carried out at atmospheric or superatmospheric pressure, the degassing chamber likewise may be dispensed with. While the distillation chamber I referred to in Figure 1 has been described oval, circle, square, or rectangle within the distilling chamber, with condensing surfaces disposed inside or outside. or both inside and outside of the oval, circle, square, or rectangle formed by the rods. Since the heat is supplied to the oil prior to the formation of the vaporizf ing film, the support rods never acquire a temperature higher than that of the oil film which l y they support. Therefore, decomposition of the passed from chamber I5 by means of valve-controlled pipe I1 into the upper or distributing section of distilling chamber I above the apertured partition 3. By regulating the rate of pumping a constant head of oil may be maintained above the partition while the oil is fed through the apertures l in a plurality of ne streams which coalesce immediately below the partition and form a thin film or sheet across the space between the guide support rods 5. The chamber I is maintained at the desired reduced pressure,

-.for example, 10 to 15 microns, by means of a vacuum pump connected through pipe I0. The

heated oil continuously supplied to therods 5 flows downwardly in a continuous film between rods 5, and during its passage a portion of the oil is vaporized by the contained heat and the vapors diffuse through the chamber, eventually coming into contact with the walls of the chamber and condensing thereupon. The chamber walls may be maintained at a suitable condensing temperature by circulating through the Jacket 2 a cooling medium such as water or other agent. Since the most volatile constituents of the oil are the first to vaporize and diifuse from the film, the most volatile condensate vwill be drawn olf from the uppermost trough 6,

and the progressively less volatile condensates will be drawn ofi' at. the successively lower troughs. In the apparatus illustrated, 3 different condensate fractions may be obtained by drawing from valve-controlled pipes 1, or if desired, the condensates may be drawn from valvecontrolled pipes 8 ,and combined into a. single condensate in manifold '9, which condensate is then removed to storage not shown. The vaporizing oil film passing downwardly between rods 5 thus becomes progressively denuded of volatile constituents, and drains olf thev lower ends of the rods into the bottom of chamber I as undistilled residue. Such residual oil or bottoms is withdrawn from chamber I by means of valvecontrolled pipe I8 and may be sent to storage,

or all or a portion of such residue may be returned by means of valve-controlled pipe I9 to pipe II for recycling, to the distilling chamber, with or without fresh-charge oil. In the event that the charge oil is relatively free of dissolved oil and deposition of carbonaceous materials upon the rods is kept at a minimum.

Another modification of a distillation chamber and attendant equipment is illustrated in Figure 2 of the drawing.

Referring to Figure 2, a cylindrical chamber I is provided in its upper portion with a partiltion 3' extending over'the cross-section of the chamber. The partition is provided with a plurality of apertures 4' extending in a line across the diameter of the partition. Suspended vertically from the partition adjacentA the end apertures thereof are two support rods 5' spaced hor- .izontally from one another, the lower ends of which terminate within a collecting funnel 2i. 0n either side of rods =5 and in a plane spaced horizontally from said rods, are a second pair of support rods 22 extending upwardly from the bottom of cham-ber I' and terminating beneath the partition 3. Disposed above the ends of rods 22 and in the same plane is a pipe 23 provided with a plurality of apertures 24, the end of such pipe extending through the wall of chamber i. At the upper section of chamber I' below partition 3' is provided a relatively large diameter pipe I0' connecting with means for reducing the pressure within the chamber. Such means (not shown) comprises any suitable type of vacuum pump.

In operation, a distillable organic substance, for example, a crude residuum obtained from petroleum is supplied from a source not shown through valve-controlled pipe II and is pumped by pump I2' through tubular heater I3 wherein the temperature of the oil is raised, for example, to 400 F. Since lt is desired to carry outv s partition 3'. By regulating the rate of pumping, a constant head of oil may be maintained above the partition while the oil is fed through the apertures t' in a, plurality of fine streams which coaiesce immediately below the partition and form a thin iilm or sheet across the space between the support rods 5. maintained at the desired low pressure, for example, 5 microns, by means of a vacuum pump connected through pipe ill. The heated oil continuously supplied to the rods 5 flows downwardly in a continuous film between rods il', and during its passage a portion of the oil is vaporized by the contained heat and the vapors diffuse through the chamber. To effect condensation o these vapors, a liquid having a low vapor pressure is supplied to distributing pipe 23 whence it is delivered through apertures it to support rods it, whereby there is formed a condensing liquid film flowing downwardly between rods 22. The condensing liquid, being at a lower temperature than the oil vapors, effects cooling and condensation of the vapors, the resulting oil condensate traveling downwardly together with the condensing liquid film. Since the vaporizing hlm between rods 5' and the condensing film between rods Z2 are traveling parallel to one another and are in close proximity to but out of contact with one another, condensation of the vapors is efficiently carried out. The film of undistilled residue reaching the lower end of rods b' drains therefrom into collecting funnel 2l and is withdrawn through pipe 24, and may be passed to storage through valve-controlled pipe 25. .Or, all or a portion of the undistilled residue may be returned by means of valve-controlled pipe 26 to pipe il' for recycling, with or without fresh charge oil, to the distributing section of chamber i' above partition 3. The condensing liquid film and the condensate dissolved or entrained therein, upon reaching the lower end of support rods it, drains therefrom into the bottom of chamber i' and is withdrawn by means of valve-controlled pipe il and may be passed to storage or to further treatment through valve-controlled pipe 2B. lin the event that the condensing liquid consists of the oil condensate itself, a portion thereof may be passed from valve-controlled pipe 21 by means of pump 2s through cooler 3U and valve-controlled pipe 3i to the distributing pipe 23, the remainder being passed from the system through valve-controlled pipe 28. If, on the other hand, the condensing liquid comprises a low vapor pres'- sure fluid other than the condensate, such fluid may be supplied from a source not shown by means of valve-controlled pipe 32. Should the distillation be carried out at atmospheric or higher pressures, the condensing liquid need not have a low vapor pressure, i. e.. water or other uids may be used. While, in Figure 2, only one condensing lm'has been shown, it is, of course, desirable to provide a second condensing hlm on the opposite side of the vaporizing film. This may readily be accomplished by providing a second set of support rods similar to rods 22 to support the second condensing film, the condensing liquid distributing apparatus being similar to that already shown.

A further modication of apparatus suitable for carrying out the process of the present invention is illustrated in Figure 3 o! the drawing, in which the distillation chamber is shown as an end view rather than as a side view as in Figure 2.

The chamber i is 6' l, 3i is provided in its upper portion with a partition 34 extending over the cross-section of the chamber. 'Ihe partition is `provided with a plurality of series of apertures 35 extending transversely across the partition, each line or series of apertures being horizontally spaced from one another. Disposed vertically at each end ot each series of apertures are support rods 3b, the lower ends of which terminate within alternate collecting channels $1 formed by partitions 3@ extending transversely across the bottom of chamber M. Also disposed vertically within` chamber 33 between each of the sets of support rods 3d and spaced horizontally therefrom, are a plurality of support rods 39, one rod being placed at each end of each apertured distributing pipe 4t, a plurality of which are connected to manifold 4i. The support rods 39 terminate within alternate collecting channels 42. At the mid-section of the back wall of chamber 23 are provided a plurality of relatively large diameter openings 43 connected to pipe 4d, which in turn leads to a suitable means for evacuating chamber 33, such means comprising a vacuum pump not shown.

'I'he distilling chamber 33 comprises, in effect, a rectangular vessel containing alternate sets of support rods 36 and 39 for supporting alternate vaporizing and condensing lms, respectively, the material to be distilled being supplied labove apertured partition 34, and the condensing liquid beingsupplied through the apertured pipes 40. The condensing liquid and condensate is collected and withdrawn from-channels 42, and the undistilled residue is collected and withdrawn from channels 31, as will be described in detail hereinafter. In operation, a distillable organic substance. for example, a high viscosity hydrocarbon lubricating oil stock, is supplied from a source not shown through valve-controlled pipe 4l and is pumped by pump 46 through a heating means such as tubular heater 41 wherein the temperature of the oil is raised, for example, to 330 F. The heated oil is then passed through valve-controlled pipe ll8 to degassing chamber 49 connected to a vacuum pump (not shown) by means of pipe 50. Herein, the hot oil is subjected to reduced pressure and the dissolved gases are removed. The degassed oil is passed from chamber 48 through valve-controlled manifold 5i into the upper section of distilling chamber 33 above I the apertured partition 34. If the oil is already degassed or if the distillation was to be effected at atmospheric or higher pressure the degassing chamber may be dispensed with, and the oli delivered through valve-controlled pipe 56 to manifold 5|. By regulating the rate of pumping, a constant head of oil may be maintained above the partition I4 while the oil is fed through the plurality of series of apertures 35 to the support rads 36, thereby forming a plurality of continuously owing vertical iilms supported by rods li. The chamber 33 is maintained at the desired reduced pressure, for example, 50 microns, by means of a vacuum pump connected to pipe 44. During the passage of the supported oil lms downwardly throgh the chamber 33, a portion oi the oil is vaporized by its contained heat, and the vapors diffuse from the lms into the chamber. The illms of undistilled residue or bottoms" reaching the lower ends of rods 3B drain from the rods into channels 31 and are withdrawn through manifold 52. The bottoms may be sent to storage through valve-controlled pipe 53, or all or any portion of such bottoms" may be returned through valve Il to pipe Il for recycling, with or without fresh charge oil. to the distillation chamber for furtherdistillation.

To effect condensation oi' the vapors diffused from the vaporizing films, a condensing liquid of low vaporl pressure is supplied through manifold 4i to the apertured distributing pipes Il, and is fed from the apertures onto the rods Il. thereby forming a plurality of continuously flowing vertical condensing films supported by the rods 3l. The condensing liquid, being at a lower temperature than the oil vapors, effects cooling and condenstion of the vapors, the resulting con densate traveling downwardly together 'with the condensing film. The condensing liquid films and the condensate dissolved or entrained therein,

bottom of column I l, cooled. and passed to storage through valve-controlled pipe 1l. 0n the other hand, if the condensing liquid is higher boiling than the oil condensate, the condensate will b' vaporized and taken overhead and the condensing liquid will be drawn at bottoms.

In the operation of the distilling apparatus at low pressures, for example, 250 microns or less.

upon reaching the lower ends of support rods Il drains therefrom into the channels land is withdrawn therefrom through manifold I5. De-

pending upon the nature of the condensing liquid,

and then supplied through valve-controlled pipe Il to manifold 4I for reuse as condensing liquid.

On the other hand, if the condensing iluidis relatively immiscible with the oil condensate, the lmmiscible mixture after passing through cooler ".,is introduced through valve-controlled pipe 02 into settling vessel or separator Il wherein l st'ances at temperature up to the decompositionv the immiscible mixture of oil condensate and f condensing. liquid is permitted to settle and stratify into layers, the condensingliquid forming the upper layer if the specific gravity of such liquidis lower than that of the oil. v The upper layer is continuously drawn olf through valve. controlled pipe 64 and returned to manifold 4I for reuse as condensing liquid. The lower layer of oil condensate is drawn from the bottom of separator 63 by means of valve-controlled pipe II and passed to storage not shown. In the event that the oil condensate has a lower specific gravity than the condensing liquid, the connections will be reversed whereby the oil condensate is drawn from the top of the separator and the condensing liquid from the bottom of the separator for return to manifold I I.

Finally, if the condensing liquid is miscible or partially miscible with the oil condensate and has a boiling point or boiling range di'erent than that of the oil condensate, the mixture or solution of oil condensate and condensing liquid is delivered by pump 58 through valve-controlled pipe It to ,fractionating or stripping coluxnnl'l provided with bubble trays 6l, heating coil l., and dephlegmating coil 10. Assuming that .thec'ondensing liquid has a lower boiling point or range than the oil condensate, the mixture in passing downwardly through the column is subjected to fractionation, the necessary heat being supplied primarily by the heating coil 89. The condensing liquid is vaporized and fractionated from the oil condensate, the vapors being taken overhead through pipe 1I, condensed in condenser 12, and the resulting liquid stored in tank 13 from which it may be returned by pump 14 through valvecontrolled pipe 15 to manifold 4| for reuse as condensingliquid. The oil thus separated by the fractionation operation may be drawn from the it is necessary to employ condensing liquids having a relatively low vapor pressure at the condensing temperature, otherwise a low pressure could not be maintained in the apparatus. However, if the temperature of the condensing liquid film is very low, the actual boiling point of the condensing liquid is of little consequence, since its vapor pressure would necessarily be low. Buitable condensing liquids include the condensate, per se, whether it be hydrocarbon oil or other condensate produced lby the distillation. Various other compounds may also be employed, such as glycerol, glycol, the polyglycerols and DOlyslycols, organic esters of the acids of phosphorus, phthalic acid esters of aliphatic and aromatic alcohols including ethyl hexyl phthalate, ethyl lactate, fatty oils, and the like. When the condensing liquid temperature is maintained at a low level, more volatile liquidsmay be utilized, including halogenated hydrocarbons, aliphatic alcohols. etl'iers.l ketones, nitroparaillns, .nitro aromatica, hydrocarbon distillates, gas oil, water, aqueous solutions of soluble salts, sugar solutions, etc.

t The method of the present invention is applicable to the distillation of distillable organic subtmperature at the prevailing pressure. In general, vevaporative distillation may be effected at temperatures up to 600 F., temperatures of the order of 250 F. to 400 1lb-being suitable for most hydrocarbon oils of substantial viscosity and boiling point, pressures being of the order of microns or less, and preferably l0 microns or less. It is. of course, obvious that the distillation process may be carriedout not vonly in a single continuous unit such as shown in Figures i, 2, and 3, but also in a plurality of such units in series or parallel operation. In series operation the undistilled residue from the first unit may be subjected to further distillation in a second unit at the same temperature and at a lower pressure, or at a higher temperature at the same o r lower pressure. The undistilled residue from the second unit may be charged to a third unit and the distillation continued, such process being repeated until further distillation becomes impractical.

While the present invention is particularly applicable to the evaporative distillation of organic compounds, `for example, oils, fats, waxes. and resins, such invention may be likewise employed in the distillation of inorganic substances or mixtures, including sulfuric acid; phosphoric acid; sulfuric acid contaminated with hydrocarbons. hydrocarbon polymers, or esters: sulfuric or phosphoric acid sludge from the processing or refining of petroleum or other hydrocarbons: decomposable inorganic salt solutions, and the-like.

The apparatus illustrated in Figures 1, 2, and 3 is, of course, capable of being modified in many ways in order to obtain the highest operating efficiency, depending uponthe nature and properties of the material to be distilled. For example. depending upon the viscosity andthe rate of charge of the material as well as the pressure under which the distillation is conducted, the width of the vaporizing film may vary from several inches to several feet. At low pressure, wider films may be employed, since there is less g disturbance of the lm, i.`e., weaving or biliowing,

than at atmospheric or higher pressures.v Furthermore, the length of the vaporizing film may vary from a iew feet to l or 20 feet or more, depending upon the rate of charge and the volatility of the material. The strength of the ,vaporiaing hlm may be increased by the addition oi? surface tension reducing agents such as soaps, fatty acids, and esters which may remain in the vaporizing film during distillation. Moreover, various means may be employed in distributing the material comprising the vaporizing film and the condensing iilm. For example, in lieu of a partition or pipe provided with a plurality ci apertures as shown in Figures l, 2, and 3, other means such as weirs. dams, nozzles, or short tubes may be utilized. It of course will be ap- I parent that the apertures 4 will be reasonably closely spaced and of relatively small diameter, dependent upon the material to be distilled. In the example which follows, a series of l?! inch diameter openings spaced on Vg inch centers was employed.

The results obtained in the practice `of the present invention are given in the following examples in which a viscous hydrocarbon oil, after degassing, was distilled in an apparatus similar to that shown in Figure 1 of the drawing, the entire oil condensate being taken as a single fraction. vSuch examples are illustrative only and are not to be construed as limiting the scope of the invention. The vaporizlng film was y28 inches in length and 1% inches in width, giving a total vaporizing. surface of 0.632 square feet. l

The properties of the charge oil and the resulting distillate, as well as the operating conditions are tabulated below.

. rli'he method and apparatus of the present invention present several advantages over the methods and apparatus heretofore known to those skilled in the art. More particularly, the preheating of the material to be distilled prior to forming same into a vaporizing iilm and thus utilizing the contained heat to effect distillation avoids the use of internal heaters or solid heated surfaces which are prone to decompose the material to be distilled, thus causing deposition and accumulation of coke or carbonaceous substances upon the heating or vaporizlng surfaces. Furthermore, the use of preheated free films for vaporizing surfaces, which lms are not brought into contact with a heat-supplying surface aftery formation, not only avoids the decomposition and deposition of coke or carbonaceous substances, but

Filtered Pennsylvania Residuum Charge Oil: A. P. I. Gravity degrees.. 304 0 26.9 SU Via/100 F...- seeonds.. 592 2322 SU Via/210 F... -.do,..-. 6l 148 volume @target .ce 4140 4140 i Distillation Temp -.F.. 210-260 290-352 Distillation Pressure.. microns.. l5 20 Eistillate:

A. P. I. Gravity. .-..degrees.. 30.7 29.3 SU Via/100 F... ..Sec0nds. 116 235 SU Via/210 F..- ....d0.... 4l '48 Volume Distillate cc.. 243 340 Bottoms: v

A. P. I. Gravity. degrees.- 28. 7 26.6 SU Via/100 F... seconds.. 761 2384i SU Via/210 F... do.-.. 6l 151 Volume Bottoms ..cc.. 3870 3540 for a film of given dimensions, provides double the vaporizing surface since vaporization takes place from both sides of the guided free film, whereas in films flowing over solid surfaces, vaporization may only take place from the surface not in con- -tact with the solid.

will vaporize, forming the heated substance into4 a vertical, downwardly-moving, free-owing nlm having two exposed surfaces, each in close pronimity to and out of Contact with a condensing surface. supporting the illm at its vertical edges throughout the length of its downward travel, thereby causing it to continue unbroken throughout the length of its travel, vaporizing at least a portion of the substance from the flowing film, and condensing the vapors upon the condensing surface.

2. The method of effecting evaporative distillation of a distillable substance which comprises heating the distillable substance `to a temperature at which at least a portion thereof will vaporize, forming the heated substance into a vertical, downwardly-moving, free-flowing film having two exposed surfaces, each in close proximity to and out of contact with a condensing surface, supporting the film at its vertical edges throughout the length ofA its downward travel,

thereby causing it to continue unbroken throughout the length of its travel, vaporizing at least a portion of the substance from the flowing nlm, condensing the vapors upon the condensing surface, and separately collecting said condensate and unvaporized portion of said substance.

3. The method of eecting evaporative distillation lof adistillable substance which comprises heating the distillable substance to a temperature at which at least a portion thereof will vaporize, forming the heated substance under subatmospheric pressure into a vertical, downwardly-moving, free-flowing film having two exposed surfaces, each in close proximity to and out of contact with a condensing surface, supporting the film -at its vertical edges throughout the length of its downward travel, thereby causing it to continue unbroken throughout the length of its travel, vaporizing at least a portion of the substance from the owlng film, and ccndensing the vapors upon the condensing surface.

4. The method of effecting evaporative .distillation of a degassed distillable substance which comprises heating the degassed distillable substance to a temperature at which at least a portion thereof will vaporlze, forming the heated substance under subatmospheric pressure into a vertical, downwardly-moving, free-flowing nlm having two exposed surfaces, each in close proximity to and out of contact with a condensing surface, supporting the film at its vertical edges throughout the length of its downward travel, thereby causing it to continue unbroken throughout the length of its travel, vaporizing at least a portion of the substance from the flowing iilm,

condensing the vapors upon the condensing suri'ace, andE separately collecting said condensate and unvaporized portion oi' said substance.

SEYMOUR. W. FERRIS. EDWARD R.. LAMSON. DOUGLAS M. SMITH.

REFERENCES CITED UNITED STATES PATENTS Number Name Date Hickman May 17, 1938 Number Name Date Hickman et al Aug. 9, 1939 Waterman et al Sept. 6, 1938 Hickman 1---" Aug. 13, 1940 Voorhees .f Dec. i0, 1940 Houghton Jan. 21, 1941 Litton Dec. 16, 1941 Hickman Mar. '1, 1944 Holder Nov. 21, 1944 Heckler Feb. 27, 1945 Litton May 1, 1945 

